1. Field of the Invention
The present invention relates to a probe of an endoscope, which has an image receiving optical element, including an image guide fiber bundle and an imaging device, and an illumination optical system provided with a light guide fiber bundle.
2. Description of the Related Art
Usually, a medical endoscope for observing the inside of a human body, and an industrial endoscope for observing the inside of a machine, are provided with an illumination optical system and an image receiving optical element. Namely, the inside of the body or the machine is illuminated by the illumination optical system, and an image of the observed object illuminated by the illumination optical system is received and transmitted to an operation unit of the endoscope by the image receiving optical element. The endoscopes have a probe, which is inserted into the body or the machine and includes a flexible tube, a bendable tube, and a distal end. The inside of the probe is essentially provided with a light guide fiber bundle, which is a part of the illumination optical system, and an image receiving optical element. The image receiving optical element of a fiber-optic endoscope is an image guide fiber bundle,which senses an observed object image formed by an objective optical system and transmits the image as optical information. The image receiving optical element of an electronic endoscope is an imaging device, which senses the observed object image and transforms the image to an electric signal.
In the light guide fiber bundle, as the illumination sectional area (i.e., the sum of the sectional area of cores of optical fibers forming the light guide fiber bundle) becomes large, the illumination amount of light which can be transmitted becomes great, and thus the observed object can be illuminated with bright light. Conversely, in the image receiving optical element, as the light receiving sectional area (i.e., the sum of the sectional area of cores of optical fibers forming the image guide fiber bundle, or the sum of areas of the light receiving cells, except the transfer gates, on the light receiving surface of the imaging device) becomes large, the amount of light which can be received becomes great, and thus a bright image can be transmitted. Namely, if the illumination sectional area of the light guide fiber bundle is made as large as possible while the light receiving sectional area of the image receiving optical element is made as large as possible, the observed object can be observed as a bright object.
On the other hand, the outer diameter and the inner diameter of the probe of the endoscope are limited, because the probe is inserted into a narrow internal space of a body, a machine etc., and because the inner wall is provided with a synthetic resin tube etc. so as to protect the light guide fiber bundle, and the image receiving optical element. Further, other than the light guide fiber bundle and the image receiving optical element, various contents including wires for bending the bendable tube, a biopsy forceps channel, and air and liquid supply tubes, in the case of a medical endoscope, for example, are housed in the probe, in which the inner diameter is limited. Therefore, the sectional area of the space, in which the light guide fiber bundle and the image receiving optical element can occupy, i.e., the accommodation space, is further limited.
Accordingly, when accommodating the light guide fiber bundle and the image receiving optical element in the probe, in which the sectional area of the accommodation space is limited as described above, a ratio of the illumination sectional area of the light guide fiber bundle to the light receiving area of the image receiving optical element should be optimized so as to maximize the brightness of the observed object image.
Therefore, an object of the present invention is to provide a probe of an endoscope, in which the ratio of the illumination sectional area of the light guide fiber bundle to the light receiving area of the image receiving optical element is optimized.
According to the present invention, there is provided a probe of an endoscope, comprising a distal end, in which an objective lens is disposed, a light guide fiber bundle and an image receiving optical element. The light guide fiber bundle supplies illumination light to the distal end. The image receiving optical element transmits an image of the observed object obtained by the objective lens. A ratio of an illumination sectional area of the light guide fiber bundle to a light receiving area of the image receiving optical element is in a range of 39:61 and 61:39.
When the range of the sectional areas is between 39:61 and 61:39, and the sum of the sectional areas of the light guide fiber bundle and the sum of the areas of the image receiving optical element is fixed, the amount of light of the observed object image transmitted by the image receiving optical element is between the maximum and 95% of the maximum. Therefore, even though the sectional area of the accommodation space of the probe is limited, a bright object can be effectively obtained.
Note that, even within the range of the ratio described above, if the illumination sectional area of the light guide fiber bundle and the light receiving area of the image receiving optical element are made equal to each other, the observed object image becomes brightest.
The image receiving optical element is an image guide fiber bundle when the endoscope is a medical endoscope, and is an imaging device when the endoscope is an electronic endoscope. When the image receiving optical element is an image guide fiber bundle formed by bundling optical fibers, the light receiving area is a light receiving sectional area corresponding to the sum of sectional areas of cores of the optical fibers. When the image receiving optical element is an imaging device having light receiving cells, the light receiving area is an effective light receiving area corresponding to the sum of areas of the light receiving cells.
Further, according to the present invention, there is provided a probe of an endoscope, comprising a light guide fiber bundle and an image receiving optical element. The light guide fiber bundle supplies illumination light to the distal end of the probe, so that the illumination light is radiated onto and reflected by the observed object. The image receiving optical element receives the reflected light. A ratio of an illumination sectional area of the light guide fiber bundle to a light receiving area of the image receiving optical element is in a range of 39 to 61 and 61 to 39.